A valve with a canister for dispersing materials into a liquid is shown in U.S. Pat. No. 4,662,387. Such dispersal valves are used to disperse a solid dispersant into a liquid. Typical applications are to disperse chlorine or bromine into a water supply to disinfect the water. In general, the prior art in line dispersal valve controls the rate of dispersant by controlling the amount of water flowing through a canister in the dispersal valve. The canister includes a removable top for inserting additional dispersant material in the canister. The present invention is an improvement to the dispersal valve shown in U.S. Pat. No. 4,662,387 by providing more precise control of the rate of dispersal over an extended period of time as well as providing a visual indication of when the dispersant in the canister is used up.